Sandblast stencil



. Aug 1941- A. J. WARTHA 2,251,646

SANDBLAST STENCIL Filed May 25, 1939 Patented Aug. 5, 1941 UNITED STATES PATENT OFFICE,

SANDBLAST STENCIL Alfred J. \Vartha, St. Paul, Minn., asslgnor to Minnesota Mining & Manufacturing Company, St. Paul, Minn., a corporation of Delaware Application May 25, 1939, Serial No. 275,596

7 Claims.

This invention relates in general to vulcanized sheet material of a nature to be inherently resistant to abrasion, such as it would be subjected to when used as a stencil material for sandblasting operations, and especially to such materials provided with an adhesive coating which is also characterized by resistance to abrasion and is desirably of a pressure-sensitive nature, Furthermore, the adhesive is preferably water-insoluble and normally non-drying. While the invention isdescribed and claimed with respect to a sheet material particularly adapted for use in making stencils, it will be understood that the material may be employed for other purposes and the invention therefore finds a wide field of utility.

This application is a continuation-in-part of my copending applications, Ser. No. 659,110, filed March 1, 1933, Ser. No. 87,945, filed June 29, 1936, and Ser. No. 218,242, filed July 8, 1938, and relates particularly to an improved sheet composition which may or may not be provided with tion, it being understood, however, that such limited fields of specific use are cited merely for purposes of illustration as examples of the utility of the invention in its several phases. A prime requisite of stencil material to be used in inscribing stones, such as granite or marble, by sandblasting, is that it must be sufliciently strong and resilient to resist abrasion by a stream under 7 an air pressure of 100 pounds. It must be flexible to conform to extremely uneven surfaces on which it may be applied. It must be tough enough to withstand abrasion andyet it must be capable of being readily and accurately cut to form a stencil aperture of an intricate design. It must adhere to the surface to be inscribed firmly enough to prevent its displacement during the sandblasting operation and yet not so strongly as to injure the surface or cause adhesion Other objects and advantages of the present invention reside in the provision of a stenciling sheet which possesses unusual durability under the high pressures employed in pressing blasting; the provision of an improved adhesively coated stenciling sheet in which quick application of the same to a desired surface, and particularly a cold surface, may be made in any kind of weather; the provision of a stenciling sheet and adhesive therefor in which the adhesive and the sheet are non-hardening and in which the adhesive is pressure-sensitive; the provision of an improvedform of stenciling sheet which permits, in high-pressure sand-blasting methods, of high ly accurate work by the operator and to permit the operator to do what is known as fine edge carving; the provision of an improved form of stencil sheet in which the adhesive employed possesses a high degree of tenacity for the surface to which it is applied, thus preventing the stencil from leaving the stone while blasting and. at the 1 same time, in which the adhesive will not ofl'set onto the softer stones or pull away particles of the stone when it is removed therefrom.

As an example of a preferred form of the present invention, reference may be had to the ac-' companying drawing, in which Figure 1 is a plan view of a sheet of the stencil 7 material with apertures cut therein to provide a design and adapted to be used as a stenciling sheet;

Figure 2, an enlarged sectional view of the sheet showing the backing and layer of pressure-' sensitive adhesive;

Figure 3,a sectional view'of the stencil sheet applied to a stone surface; A

Figure 4, an enlarged fragmentary sectional view of the stencil sheet prior to application to a surface; and

Figure 5, an enlarged fragmentary sectional view of an alternative form of this invention.

I have found that the foregoing highly desirable results may be obtained by employing a composite backing which may be termed a compounded vulcanized rubber sheet or vulcanized rubber composition sheet and which has applied Solros, factice and beta naphthol with a suitable vulcanizing material. In this composition the whiting provides a finely divided base material which is bonded together to form a coherent mass by the vulcanized binder. Other comminuted base material, such as Dixie clay,

soapstone and the like, may be employed instead of whiting, in whole or in part. The bone glue sittings are a convenient form ofiinely divided glue which serves as-a bodying ingredient in addition to the whiting, and also gives firmness to the composite sheet which enhances the ease and accuracy of cutting apertures in the sheet to form the stencil. Factice is a vulcanized vegetable oil which mixes evenly with the rubber to increase the homogeneity of the mass and also serves to modify and reduce the nerve of the rubber. This latter function is important in that the ordinary characteristics of rubber as to toughness and elasticity are not desirable in this composite sheet as they would cause the sheet to be difllcult to cut accurately to the desired design. Vulcanized vegetable oils (factice) have been found to be particularly suitable for this purpose. For example, such-vegetable oils as vulcanized linseed oil, tung oil, cottonseed oil, corn oil. and sunflower seed oil have been found to be satisfactory.

The reduction of the nerve of the rubber is further accomplished by the intensive milling in the preparation of the composite material as hereinafter disclosed. Solros is a heat treated wood rosin used in this composition as a tempering agent particularly during the milling process. Beta naphthol is an antioxidant used to prolong the life of both the rubber and the glue of this composition.

While the proportions of these ingredients may be varied within reasonable limits, I have found proportions by weight according to the following formula to give a desirable composite sheet material.

Foams A Pounds Bone glue siftings 20 Latex crepe rubber 20 Whitin t 60 Solros .9 Factice 5 Beta nap .2

For .my purposes it is preferred to place the rubber in a mill and then mill it until the mass follows the mill roll and gives the appearance of a smooth film covering the roll. This takes approximately ten minutes of milling time.

The bone glue siftings are then added and the rubber and glue, in substantially equal amounts, milled for approximately thirty minutes. From time to time the mass may be treated with steam applied directly thereto, thus moistening the glue content and causing the same to more rapidly melt into and mix with the rubber.

I then mix thoroughly together the factice, whiting, Solros and beta naphthol and when well mixed they areadded to the rubber-glue mass. This mass is then milled under steam application until the entire batch is thoroughly homogenized.

When the composite mass made according to the above formula has been thoroughly mixed, it is then sheeted or calendered to form a sheet of the desired thickness, which, for example, may be approximately .035 inch. After cooling, the sheet is treated with a vulcanizing solution comprised of one part sulfur chloride and eight parts hydrocarbon liquid with which the sulfur ch10- ride is miscible, as benzol or the like. Preferably, to apply the vulcanizing solution, the compounded sheeting is laid out and a coating of sulfur chloride is brushed or sprayed onto its exposed surface and allowed to stand until vulcanized. However, I may immerse or subject both surfaces to the solution to obtain a faster and more thorough vulcanization upon evaporation of the solvent and reaction of the sulfur chloride, with a vulcanizable material contained in-the composite sheeting.

Alternatively, when a compounded backing completely vulcanized is preferred, I incorporate with the Formula A, following its compounding, stock curing or vulcanizing materials of the following character expressed in proportionate parts by weight based on parts rubberas contained in the aforementioned formula:

- Parts Zinc oxide 5 Stearic acid 3 Sulfur, 3

Accelerator "D. P. G. (diphenylguanidine) 1 Parts Formula A s 530 Zinc oxide 25 D. P. G. accelerator 1 Sulphur 4 which may be mixed by milling for approximately 30 minutes, then sheeting it .and vulcanizing it at 250 F. for two hours.

As a substitute for the vulcanizing agents expressed above, I may use a sulfur bearing compound such as Tetrone A (dipentamethylenethiuramtetrasulflde) or the like milled directly into the compounded base in the proportions of .53 ounce per 19 lbs. of the compounded plastic stock with subsequent sheeting and vulcanizing at a temperature of approximately 250 F. for a period of two hours. t

The antioxidant, vulcanizing agents and their accelerators as expressed are illustrative examples and it is to be understood that other similar materials may be substituted by proper selection of such agents well known to the art.

While the composition of Formula A is in proportionate parts as preferred, I have found that I may vary the ingredientsto the following extent and obtain a workable sheet:

Parts Bone glue sifting 10 to 25 Rubber content 15 to 40 Whiting 60 to 75 Rosin .9 to 1 Factice 5 to 20 with no variation in the aging inhibitor, the vulcanizing materials to be added proportionately as well known in the art.

The sheeted backing for stenciling and other purposes may be calendered to any thickness desired; however, for stenciling purposes the thickness is approximately .035 inch when used with a temporary liner as hereinafter described, but for other purposes and including stenciling, the compound may be sheeted to .022 inch thickness more or less as desired, as, for example, when used with a permanently attached liner as hereinafter described.

After the vulcanized backing has been formed, the resultant sheet, as in the first instance, is coated on the unvulcanized side with an adhesive of a character of the formulae hereinafter set out, or when uniformly vulcanized, on either side, the adhesive in either case being warmed on the mill just prior to its application to the backing sheet. A liner is employed to prevent the adhesive side from sticking to the backing sheet.

The formulae for the adhesives call for the ingredients which are similar to those used in the backing. Due in part to this similarity and in part to the nature of the adhesive compound, the bond which results when the adhesive is applied to the backing is ofsuch strength that it is practically impossible to cause subsequent separation by mechanical means. This condition prevents lamination or separation even under the most adverse treatment.

An illustrative formula for an adhesive by weight may be as follows:

FORMULA B Pounds Latex crepe rubber 40 Zinc oxide 20 Whiting 20 Solros rosin 26.7 Beta naphthol .4

The process of making the adhesive which I prefer to employ for the purpose of this invention is carried out by running the latex crepe material for six or seven minutes in the mixer. The pigments, such as the zinc oxide and whiting, are then added, together with the beta naphthol, and the mixing carried on until the pigments are completely dispersed throughout the latex crepe. I then add the Solros rosin and subject the whole batch to a thorough mixing. The batch is then removed from the mill with a scraper and may be stored in trays with a powdered liner until ready for application to the sheeted backing.

In this formula the relatively large ratio of pigments such as zinc oxide and whiting serve to make the adhesive blast-resistant, and the Solros rosin in this case serves as a tack-producing ingredient to give the adhesive the desired normally tacky character.

A softer pressure-sensitive adhesive particularly applicable to cold surfaces as cold stone, or the like, and one which aids in the use of a cheaper liner, as hereinafter described may be employed, is a composition of the following character:

Foxmum C I Part 1 Smoked sheets pounds 50 Zinc oxide ounds.. 25 Pine tar pounds 3 Res ound .5 Beta naphthol pound .5 Peptizing agent grams 68 ing time usually requires a minimum of 30 minutes.

To the composition of Part 1 is further added a plasticizing agent and additional tack-producing resins in the following proportionate parts:

Part 2 Pounds Part 1 I 4.35 Plasticizer (stearic acid) .50 Rosin (water white) 1.24 Solros ros .41

FORMULA D Grams Latex crepe 1000 Zinc oxide 200 Peptizing agent 2 Antioxidant 25 Plasticizer 5 Vulcanizing agent 7 prepared by milling the crepe and zinc oxide for approximately 4 minutes at 20 lbs. steam pressure, adding the peptizing agent, such as RPA #2, a commercial mercaptan (naphthyl betamercaptan) or other well-known peptizing agents, such as are described in the heretofore mentioned patents of Williams et al., and milling the composition for approximately 20 minutes whereupon an antioxidant, such as Neozone A (phenyl alpha naphthylamine) and a plasticizer, such as stearic acid, are added and the mass milled for approximately 30 minutes. This compounded crepe composition is then removed from the milling rolls and placed in an internal mixer, such as a Baker-Perkins Mogul machine, and mixed for 20 hours at approximately 250 to'260 F. at which time the Vulcanizing agent, preferably a prepared sulfur-bearing compound as Tetrone A (dipentamethylenethiuramtetrasulfide) mixed with 500 grams of a filler, such as Dixie clay, is added with continued mixing for an additional hour or until such time as is necessary to vulcanize the adhesive. This vulcanized material is then removed from the mixer and calendered in the usual manner of calendering onto the stencil sheet backing, The filler may be omitted if desired.

The adhesive of the foregoing formulae possesses great tenacity, and I find' that, for some purposes, there must be employed a liner between the adhesive layer and an adjacent surface, such as the backing of the stencil sheet itself. For the purpose of a liner I have employed starched Holland cloth applied directly to the surface of the adhesive, as fully described in my copending applications previously referred to.

Where desired, I am able to. reduce the tenacity of the adhesive and yet have it retain the desired degree of adhesion to a surface to which it is applied by reducing the adhesive character thereof. This is accomplished, for example, by increasing the proportion of filler, 'whiting or the like, and I have found that a, liner made of paper treated with a material inactive to the adberized backing, a coating of adhesive applied to one surface thereof, and a liner of suitable material, such as starched Holland cloth, applied to the exposed surface of the adhesive. This Holland cloth liner is to be removed prior to applying the stencil to a surface to be inscribed. The stencil sheet will be provided with suitable apertures defining the outlines of the design to be cut by the sandblast either before or after it is applied to the surface to be inscribed.

1 As an alternative construction of the stencil,

and to reduce the cost of production brought about by the use of the starched Holland cloth,

and further, to avoid the diflicul-ties sometimes encountered by inexperienced workmen in removing the Holland cloth from the adhesive, I

may provide a modified structure comprising the rubberized sheeting as a backing having the adhesive applied to one surface thereof, and as a protective liner I apply a parchementized paper to the backing itself so that it is interposed be- .tween the exposed surface of the backing when the stenciling material is rolled upon itself or stored in stacks, in the manner fully described in my copending applications previously set forth. By this construction .I am enabled to avoid starch transfer, that is, particles of starch offsetting onto the adhesive when the liner is being removed. The parchmentized paper applied to the back of the backing sheet is of such a character as to be readily removable in cold water when the stencil is to be used. For this purpose I have employed a parchmentized sheet of paper treated with glycerine and primed onone side so as to have a partial aflinity for the adiacent surface of the backing and thus retain a tenacious grip thereon until immersed in cold water by the user while applying the stencil to a surface for sandblasting purposes. The composition of the primer and method of. application are set forth in my applications referred to.

Referring now more particularly to the drawing, one form of the stencil sheet is illustrated in Figures 1 to 4 and is composed conveniently of a vulcanized rubber composition backing sheet 5, made according to the formula and process herein set out, provided with an adhesive coating 6, which is of a pressure-sensitive nature and made in accordance with the formula for an adhesive herein set forth. Apertures are cut in the stencil sheet to provide the desired design, as indicated at 1, or numerals or letters as the case may be, indicated at 8.

When the sheet and adhesive are combined, they are provided with a liner of material such as starched Holland cloth,'indicated at 9 in Figures 2 and 4, to prevent excessive adhesion between contiguous layers and a consequent offsetting of the adhesive onto the backing, as hereinabove pointed out. This liner is removed before the stencil is applied to a surface In, such, for example, as is shown in Figure 3. The de sign forming apertures 1 and 8 may be cut in the stencil sheet either before application to the surface or after such application. When out before application, the liner 9 may, if desired, be left intact as shown at Figure 4.

when the stencil sheet is applied to a surface indicated at III in Figure 3, the adhesive coating tenaciously adheres to this surface, which may be the surface of a marble slab II. [The nature of the adhesive is such that it provides dams ii, at the margins of the openings 1 and 0, so that the sandblast striking the exposed surface of the slab through these openings will cut away recesses corresponding in shape to the openings. Owing to the intimacy with which the adhesive engages the surface l0, thesandblast cannot creep under the adhesive, and where. the stencil is used for paints and varnishes, the same apthe backing 5a and the-adhesive" coating in, provided with a suitable aperture 'la, representing the desired design.

The parchmentized liner I l is applied to the back of the backing 5a and is of a character which is repellent to the adhesive in, thus preventing excessive adhesion and yet permitting the stencil to be rolled or stacked in sheets. The parchmentizeds'heet Il may be provided with apertures 15 corresponding to the apertures in the stencil for convenience in identifying the stencil, though it is to be understood that the parchmentized sheet may be continuous for the reason that it is to be removed before the sandblast is applied to the surface. Additionally, the design forming apertures may be cut in the sheet after it is applied to the surface.

Whenthe stencil shown in Figure 5 is to be used, water may be applied to the liner for a minute or two, sufficient to reduce. the bond between the liner l4 and the backing formed by the primer l6, so that the liner ll may be readily removed. Owing to the moistureproof nature of the stencil itself and its adhesive, immersion in water has no deleterious effect upon the stencil structure.

The permanent adhesive protective sheet described and claimed in my copendingv patent application Ser. No. 313,370, filed January 11, 1940, may likewise be employed with the improved sheet composition described herein. In this embodiment a protective sheet comprising a unified porous paper or cloth, treated to adapt it to re.- ceive pencil or carbon impression on its exposed surface, is permanently adhered to the improved sheet composition 5. I

By virtue of the rubber content of the backing and the combining of the ingredients thereof, a tough, resilient and -distensible sheet material is produced which, because of these properties, adequately resists penetration and wearing away by the high velocity sand particles'used in sandblasting operations. Furthermore, when applied to uneven surfaces, such as curved surfaces, the distensibility of the backing and adhesive permit of the application of the stencil sheet snugly at all points so that danger of the sandblast or spray paint, or the like, flowing under the stencil is prevented, the intimacywith which the adhesive engages the surface to which the sheet is applied, together with the backing itself, serving as a dam to prevent penetration of the sand or flowing of liquids past the desired confines aiforded by the walls of the openings in the stencil.

From the foregoing it will be understood that the invention may be produced in two general forms, that is to say, the stencil sheet may be made up with a liner, such as Holland cloth, on the adhesive coated side thereof as a protection against oifsetting of the adhesive onto the back of thesheet when rolled or stacked. This lineris to be removed when the stencil is prepared for use. In the other forms of the invention the liner on the adhesive surface may be omitted and a parchmentized paper, the permanent adhesive protective sheet previously mentioned or other suitable protective material or film coating, such as a coating of shellac, cellulosic or resinous masistance to impact of abrasive particles, said sheet material including a comminuted base material bonded together by a binder, said binder com; prising major proportions of vulcanized rubber and minor proportions of factice to provide sheet material capable of being readily and accurately terial, previously described, may be applied to the back of the backing sheet and attached thereto by virtue of inherent afiinity or the afilnity which the priming solution or adhesive composition has for the backing. The latter liners adhering by means of an interposed adhesive may be removed,

if desired, by application of this water.

As an alternative formula for the composition backing, I have had success with a composition wherein the quantity of factice employed is increased to about twice that shown in the Formula A above. This gives a mass which is more readily slit, but does not have as high resistance to impact of the particles used in the sandblast.

It will be understood that the drawing forming a part of this specification is merely illustrative of certain applications of the invention and that the adhesive and the backing to which it is applied may be produced alone for certain purposes, and that Iconsider my invention as possessing novelty whether a backing or protective liner is applied or not. For example, the products may have important uses for other purposes as,in the taping field, it may be used to provide adhesive sheets or tapes as: packaging tape, masking tape, ceramic tape, electrical insulating tape, can-sealing tape, shoe tape, tape to replace viscose coverings on bottles, bookbinding tape, repair tape, frost shield tape and many others. Further, the compounded material may be used without the adhesive as, for example, to form printers rolls, protective aprons, as a packing, insulating, plating material, and in many other fields.

In the specification and claims where I refer to a blasting resistant material or blasting resistant characteristics or blasting resistance," I mean to include thereby a physical character of resiliency, deforming under the impact of an air blast and material entrained thereby, adapted to reassume its normal contour without experiencing substantial abrasion, drying, or hardening, as distinguished from an objectionable warping, shrinking, expanding, drying,

hardening and abrasion of other stenciling ormasking materials known to me, which under the cut to form a stencil aperture. 7

2. As a new article of manufacture, vulcanized sheet material having the properties of flexibility and resistance to impact of abrasive particles, said sheet material including a comminuted base material bonded together by a binder, said binder comprising major proportions of vulcanized rubber and minor proportions of vulcanized vegetable oil to provide a sheet material capable of I being readily and accurately cut to form a stencil aperture.

3. As a new article ofmanufacture, self-sustaining sheet material having the properties of flexibility and resistance to impact of abrasive particles, comprising a composition in sheet form of by weight 10-25 parts of glue and 60-75 parts of comminuted base material b nded together by a binder comprising major proportions of vulcanized rubber and minor proportions of a vulcanized vegetable oil adapted to reduce the nerve of said rubber to provide sheet material capable of being readily and accurately cut to form an aperture.

4. As a new article of manufacture, self-sustaining sheet material having the properties of flexibility and resistance to impact of abrasive particles, comprising a composition in sheet form of by weight 10-25 parts glue, 15-40 parts vulcanized rubber, 60-75 parts comminuted base material, and 5-20 parts vulcanized vegetable oil.

action of an air blast and materials entrained thereby, exhibit the objectionable characteristics referred to, after blasting. The term "sandblast stencil," or sandblast stencil sheet," as used in the specification and claims denotes sheet material intended forand suitable for use in 5. As a new article of manufacture, sheeted material comprising a flexible mass containing as ingredients thereof glue, vulcanized rubber, whiting, a resin, and factice,- and a normally pressure-sensitive rubber base adhesive coating aiilxed to one surface thereof, said composite being inherently blast resistant.

6. As a new article of manufacture, sheeted material comprising a flexible mass containing as ingredients thereof approximately 20 parts glue, 20 parts vulcanized rubber, 60 parts whiting. 1 part resin and 5 parts factice, and a normally pressure-sensitive rubber base adhesive coatinB afiixed to one surface thereof, said composite being inherently blast resistant.

7. As a new article of manufacture, a sandblast stencil sheet designed for use in cutting letters or configurations on a surface by means of sandblasting, comprising a blast-resistant. sheet and upon proper shaping thereof to control the sandblast so that it forms the desired letters or con figurations on said surface, said sheet comprising an admixture of whiting, vulcanized'rubber, glue, and at least 5% by weight of a vulcanized vegetable oil to reduce the nerve of said rubber to provide a sheet capable of being readily and accurately cut to form an aperture for said sand- 

